The proposed research offers a unique opportunity to provide exposure-response estimates between measured occupational biomechanical stressors, non-occupational physical activities, demographics, medical history, psychosocial factors; and risk of carpal tunnel syndrome (CTS), lateral epicondylitis (LEPI), and medial epicondylitis (MEPI). Three prospective cohort studies will pool data from 35 US workplaces, representing a wide range of occupations, industries, and physical exposure levels. 1,973 employees were enrolled and 1,698 were followed for up to 110 months (average follow-up = 34 months). Comprehensive data are available on each worker's biomechanical stressors, physical examination maneuvers, and median and ulnar nerve conduction studies at the wrist. Exposure-response relationships will be estimated between biomechanical stressors and the prevalence and incidence of: CTS, LEPI, and MEPI, while adjusting for relevant effect modifiers and confounders. Measures of biomechanical stressors used in this study include established models of ACGIH Threshold Limit Value (TLV) for Hand Activity Level (HAL), and the 1995 Strain Index (SI), as well as newly developed models: (i) Revised Strain Index (RevSI), (ii) Composite Strain Index (COSI), and (iii) Cumulative Strain Index (CUSI). Comprehensive physical exposure data from these studies feature: (i) individual worker exposure with changes in exposure over time, and (ii) detailed data for each combination of force, repetition, and posture (sub-task data). These data allow us to model biomechanical stressors in detail not previously possible using innovative approaches such as RevSI, COSI, and CUSI. The three sites all have comprehensive data on potential confounders and covariates including worker demographics, past medical history, non-occupational hobbies and activities, and psychosocial factors. All sites used matching case definitions for CTS, LEPI, and MEPI that included symptoms plus physical maneuvers and nerve conduction studies. Pooling existing data across the three studies will enable us to estimate the magnitude and shape of the relative risk function across a wider range of biomechanical stressors: (i) with improved confidence and precision, (ii) for workers with job rotation, and (iii) for tasks with multiple combinations of force, repetition, and posture. Results from this proposed research will help employers to design safe and productive jobs and provide public-health agencies and occupational health researchers with information to more effectively guide prevention programs.